SPC 0700Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1120 PM CST Thu Dec 10 2020 Valid 121200Z - 131200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... The risk for severe thunderstorms appears negligible across the U.S., Saturday through Saturday night. ...Synopsis... Much of the U.S. appears likely to remain most prominently under the influence of a generally zonal belt of westerlies emanating from the mid-latitude Pacific through this period. Models indicate that this regime will include a number of significant progressive short wave perturbations, a couple of which appear likely to support fairly significant surface cyclogenesis to the lee of the southern Rockies. While cyclogenesis may commence across parts of the southern Great Plains into middle Mississippi Valley today through tonight, it appears that the most substantive deepening will occur across the middle Mississippi Valley through southern portions of the Great Lakes region on Saturday. This will be accompanied by a significant cold front which is forecast to surge east of the Mississippi Valley into the Appalachians, while stalling across the lower Mississippi Valley into the southern Great Plains, Saturday through Saturday night. In association with these developments, large-scale forcing for ascent and strengthening deep-layer wind fields probably will become conditionally supportive of increasing convective potential, possibly across a sizable portion of the Ohio Valley, and perhaps the central and eastern Gulf Coast states. However, based on latest observational data and forecast soundings, a combination of weak/limited Gulf moisture return to the warm sector and relatively warm and/or warming layers aloft will considerably inhibit the risk for thunderstorm development. Thermodynamic profiles most conducive to convection capable of producing lightning may be confined to areas beneath mid-level cooling, to the north of a strong cyclonic mid-level jet streak nosing into the lower Ohio Valley by 12Z Saturday. Models suggest that this activity may be largely focused within weak elevated destabilization to the northeast of the surface cyclone, above the warm frontal zone, as the mid-level speed maximum rapidly propagates into and through the upper Ohio Valley during the day. Forecast soundings (particularly the NAM) do suggest some potential for very weak boundary-layer based destabilization within the warm sector, beneath an evolving dry slot across parts of Illinois into Indiana by midday Saturday. Given the potentially strong deep-layer mean wind fields and vertical shear, this will need to continue to be monitored in later outlooks for this period. However, guidance currently suggests that mid-level subsidence and warming will tend to inhibit boundary-layer based storm development. ..Kerr.. 12/11/2020
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